1. Field of the Invention
The present invention relates to a display driving circuit, and more particularly to a multi-display driving circuit used in a multi-display device and a method of driving a plurality of display panels.
2. Description of the Related Art
The latest electronic devices, such as G3 “clamshell” phones may have a dual display configuration including a main display panel and a sub-display panel. The sub-display panel may display subset of the information displayed by the main display panel (e.g., a relatively small amount of information compared with the main display panel). Further, the display device may have a multi-display that comprises three display panels.
For example, in the case of folding type (“clamshell”) mobile phones, the main display panel is located on the inner side of a folding cover (and displays a phone number while dialing and an elapsed time during a phone call, etc.,) while the sub-display is located on the outer side of the folding cover (and displays a caller ID, a signal reception strength indicator during standby mode, a clock and remaining battery power, etc.).
The dual display enhances the ease of use and function of products; however, the dual display may have an interface problem between a central processing unit (CPU) and two driving circuits (e.g., one driving circuit for driving each of the display panels).
FIG. 1 is a block diagram illustrating a conventional multi-display driver circuit.
Referring to FIG. 1, the conventional dual-display system 100 including a conventional dual-display driver circuit (102, 104, 106, 107). The conventional dual-display system 100 includes a first display panel 101, a first display driver circuit 102 for driving the first display panel 101, a second display panel 103, a second display driver circuit 104 for driving the second display panel 103, and a CPU 105.
The conventional dual-display driver circuit comprises a first display driver circuit 102 coupled to the CPU 105 via a first interface 106 and the second display driver circuit 104 is coupled to the CPU 105 via a second interface 107, as shown in FIG. 1.
Thus, as the number of the display driver circuits increases, the wiring complexity between the CPU and the display driver integrated circuits (IC) increases, and thus electromagnetic interference (EMI) characteristics deteriorate.
In addition, according to the trend towards multimedia, a display device may be required to output moving images having a high resolution or to output real-time images received from a camera, and thus the quantity of the data that must be transferred from the CPU to the display driver circuits has increased.
In a new data transfer standard, a conventional parallel data transfer method between the CPU and the display driver IC is replaced by a serial differential data transfer method. The serial differential data transfer method provides a high data transfer rate, a low EMI and a reduced wiring complexity. The connection wires between the baseband modem chip and the display driver IC may be greatly reduced compared to the conventional parallel data transfer method. For example, 30 to 40 wires between the baseband modem chip and the display driver IC may be reduced to just 4 wires plus power in the MDDI specification. MDDI is a high-speed digital packet serial interface, which allows for bidirectional data transfer and has a maximum bandwidth of up to 3.2 Gbits per second. This allows designs using up to 90 wires to interconnect the upper and lower clamshell through parallel interfaces to be reduced significantly. MDDI generally enables low-power, high-speed graphics performance for advanced multimedia clamshell phones equipped with high-resolution LCD displays.
Qualcomm, Inc. proposed the data transfer standard for mobile displays, known as a Mobile Digital Display Interface (MDDI). In the MDDI specification, data are transferred between the CPU (for example, a baseband modem chip) and a display driver IC using a serial differential data transfer method.
According to the MDDI specification, it is possible to achieve a maximum data transfer rate of 400 megabits/second in type 1, and a maximum data transfer rate of 3.2 gigabits/second in type 4.
However, the conventional multi-display device (e.g., the conventional clamshell phone) typically has one display driver IC that supports the MDDI interface and a second display driver IC that supports the conventional parallel data transfer interface.
For example, the first display driver IC for driving the main display panel supports the MDDI interface; however, the second display driver IC for driving the sub-display panel supports the conventional parallel data transfer interface. Thus, in the conventional multi-display device, the wiring complexity and the EMI characteristics cannot be greatly enhanced even when the display driver IC supports a serial differential interface (e.g., MDDI).